Taste receptors on the anterior tongue and nasoincisor ducts of rats contribute synergistically to behavioral responses to sucrose.

In four groups of rats, behavioral responsiveness to sucrose was tested by allowing them to lick solutions in a computer-controlled gustometer (10-s trials; 0.01-1.0 M). Rats with cautery lesions of the nasoincisor ducts (NID) behaved no differently from controls. After bilateral chorda tympani nerve (CT) section, which removes taste input from the anterior tongue (AT), rats demonstrated a marginal attenuation in their responsiveness to sucrose. Combining the two lesions, however, had the greatest effect on the concentration-response curve. By shifting the curve to the right and lowering the asymptotic licking rate, the combined lesion reduced the area under the curve by one third. The effects of the combined treatments were larger than would be predicted from the sum of either one alone. This presumably reflects the central convergence of primary afferent axons from the NID and AT. Neurophysiological data have demonstrated such convergence within the nucleus of the solitary tract.